Heretofore, conventional crank presses utilized a fly wheel and a bull or pinion gear arrangement for driving the fly wheel and with a mechanically controlled clutch for the control of the conventional crank shaft regulating the reciprocal movements of a top platen normally guidably mounted upon a pedestal for the purpose of forming work pieces with respect to a stationary platen.
Illustrative of the prior art type of mechanically operated and controlled crank press are the following U.S. Pat. Nos.:
148,626 issued Mar. 17, 1874; PA1 340,515 issued Apr. 20, 1886; PA1 653,955 issued July 17, 1900; PA1 661,794 issued Nov. 13, 1900; PA1 1,175,663 issued Mar. 14, 1916; PA1 1,773,438 issued Aug. 19, 1930; PA1 1,834,111 issued Dec. 1, 1931; PA1 1,936,410 issued Nov. 21, 1933; PA1 2,188,146 issued Jan. 23, 1940; PA1 2,249,149 issued July 15, 1941.
Some of the objections to the prior art type of mechanically operated and controlled crank press were that it incorporated no tonnage overload mechanism, had no way of providing a bi-directional low speed jog and did not have variable speed control between 3 rpm and 60 rpm.
The prior art crank presses did not have a fail-safe hydraulically operated brake and had no hydraulic unlock failure and omitted tonnage adjustment control features. These devices operated at a high noise level.